Uninterruptible Power Supply Voltage Imbalance Control
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Solution Overview
Problem
In three-phase four-wire uninterruptible power supply systems, terminal-to-terminal voltage imbalances occur between capacitors due to non-zero sum of AC currents flowing through the transformer, especially during power failures when the load current is small, leading to instability.
Innovation Solution
The system incorporates a neutral point line connected to the AC power supply and load, switches to control AC power flow, and multi-level circuits in converters and inverters to manage DC voltages, ensuring that the difference between terminal-to-terminal voltages is eliminated by controlling the converter and DC voltage converter operations based on detected voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system operates as a three-phase four-wire system with neutral point line, then the load can be supplied with stable AC power, but the terminal-to-terminal voltages of the capacitors become imbalanced due to non-zero sum of three-phase AC currents
Solution Approach 1:
The control unit continuously monitors the terminal-to-terminal voltages of the first and second capacitors using voltage detectors, calculates the difference voltage, and adjusts the converter and DC voltage converter operations based on feedback signals to eliminate voltage imbalance
Solution Approach 2:
The system dynamically adjusts operating parameters (converter and DC voltage converter operations) based on the detected voltage imbalance condition, changing the control parameters to eliminate the difference voltage between capacitor terminal-to-terminal voltages
2Use of energy by moving object
If the load current is small during power failure, then the power consumption is reduced, but the terminal-to-terminal voltage imbalance of capacitors increases
Solution Approach 1:
The control unit continuously monitors the terminal-to-terminal voltages of the capacitors and adjusts the DC voltage converter operation based on feedback to eliminate voltage imbalance even when load current is small
Solution Approach 2:
The system dynamically adjusts the DC voltage converter operation based on real-time voltage imbalance detection, making the control adaptive to varying load conditions including small load currents during power failure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively eliminates voltage imbalances between capacitors even during power failures with small load currents, ensuring stable operation in three-phase four-wire systems with transformers.
Implementation Method 1
a converter that converts AC voltage supplied from an AC power supply to first to third DC voltages
Implementation Method 2
a DC voltage converter that converts a fourth DC voltage from a DC power supply source to first to third DC voltages
Implementation Method 3
an inverter that converts the first to third DC voltages from the converter and the DC voltage converter to AC voltage and supplies the AC voltage to a load
Data Source
AI summary
In an uninterruptible power supply apparatus, in a power failure of a commercial AC power supply, a switch is turned off to electrically cut off the commercial AC power supply from an AC input filter, and a DC voltage converter is controlled such that a DC voltage that is the difference between terminal-to-terminal voltages of first and second capacitors is eliminated, and when the DC voltage exceeds a threshold voltage, a converter is controlled to reduce the DC voltage.